Rechargeable batteries include a NiyFe1-y cathode where 0≤y≤1, an anode comprising a current collector, a porous separator positioned between the cathode and the anode, and an electrolyte comprising MAlX4, wherein M is Na, Li, K, or a combination thereof, and X is Cl, Br, I, or a combination thereof, and wherein the electrolyte is a solid at temperatures less than 50° C. The batteries are temperature activated. The electrolyte temperature is increased above its melting point while charging and reduced below the melting point for energy storage, such as seasonal energy storage. The electrolyte temperature is increased above the melting point again to discharge the battery.